In recent years, in development of science and technology aimed at extremely fine materials, such as nanoscience and nanotechnology, it has been proved that materials and devices having various new functions and properties can be formed by designing structures of atoms, molecules, or assemblies thereof with about several nm size. In this case, in order to induce a desired function and property, it is important to precisely control an arrangement state and assembly state of atoms or molecules.
As a material which satisfies this requirement, fine particles with a size of about several nm, i.e., nanoparticles, attract attention. In order to more effectively exhibit the characteristics of nanoparticles, it is important for the nanoparticles to be independently present and have good dispersibility without aggregation of the nanoparticles. In addition, in this specification, a size of 1 nm to less than 1 μm, typically about several nm to several tens nm, is referred to as “nanosize”, and a member having the nanosize is named by adding the prefix “nano”, for example, named “nanoparticles”.
For a method for producing nanoparticles, various investigations have been made. At present, synthesis by various solution methods or vapor-phase methods is capable of not only controlling the particle size but also forming a monodispersion with a uniform size. In particular, unlike bulk materials, fine particles having a particle size of 10 nm or less not only have a very large surface area per unit mass but also exhibit a specific property due to the size, which is called a “quantum size effect”. Therefore, synthesis is attempted by using various materials, and approaches to application to sensors, optical materials, electronic materials, battery material, and catalysts are made with basic research for elucidating new phenomena.
Although the characteristics of materials and devices composed of nanoparticles may be determined by the properties possessed by each fine particle, materials bonded to the surfaces of fine particles and an arrangement of fine particles, and further a structure and size of an assembly of fine particles frequently greatly influence the characteristics and contribute to effective improvement in performance.
For example, in an optical material or conductive material using nanoparticles, the distance between the fine particles is an important factor which determines the characteristics. In addition, it is considered to be advantageous for a sensor to have a structure which increases the frequency of collision between a material to be sensed and nanoparticles in a liquid phase or vapor phase, and for a catalyst to have a structure which increases the frequency of collision between a reactant and nanoparticles. In addition, in chemical vapor deposition of carbon nanotubes starting from nanosized catalyst metal fine particles, an arrangement of the nanotubes is directly determined by an arrangement of the metal fine particles (refer to, for example, Japanese Unexamined Patent Application Publication No. 2003-183012).
Therefore, in view of application of fine particles such as nanoparticles, a technique for arranging fine particles on a substrate, in addition to synthesis of the fine particles, becomes important.
A top-down micromachining technique represented by a lithography method and a probe drawing method is also effective for fine particles. For example, fine particles can be selectively arranged in a specified region on a substrate by a method of forming a micro pattern of a self-organizing film or the like on the substrate so that the substrate has surfaces having different interactions with the fine particles, and then fixing a fine particle layer only to a surface with strong interaction.
On the other hand, a bottom-up approach uses a method using a very small mold, represented by an in-print method disclosed in Non-Patent Literature 1 described below and a micro-contact method disclosed in Non-Patent Literature 2 described below.